Fix the CanvasBackend size bug

Author: 38

examples/wasm-demo/src/func_plot.rs

@@ -10,6 +10,7 @@ pub fn draw(canvas_id: &str, power: i32) -> DrawResult<impl Fn((i32, i32)) -> Op
     root.fill(&WHITE)?;
 
     let mut chart = ChartBuilder::on(&root)
+        .margin(20)
         .caption(format!("y=x^{}", power), font)
         .x_label_area_size(30)
         .y_label_area_size(30)

examples/wasm-demo/www/index.html

@@ -12,7 +12,7 @@
 	<main>
 	    <h1>Plotters WebAssembly Demo</h1>
 	    <div id="coord"></div>
-            <canvas id="canvas" width="600" height="400"></canvas>
+        <canvas id="canvas" width="600" height="400"></canvas>
 	    <div id="status">Loading WebAssembly...</div>
 	    <div id="control">
 		<label for="plot-type">Demo: </label>

examples/wasm-demo/www/index.js

@@ -30,14 +30,13 @@ function setupUI() {
 
 /** Setup canvas to properly handle high DPI and redraw current plot. */
 function setupCanvas() {
-    const dpr = window.devicePixelRatio || 1;
+	const dpr = window.devicePixelRatio || 1.0;
     const aspectRatio = canvas.width / canvas.height;
-    const size = Math.min(canvas.width, canvas.parentNode.offsetWidth);
-    canvas.style.width = size + "px";
-    canvas.style.height = size / aspectRatio + "px";
-    canvas.width = size * dpr;
-    canvas.height = size / aspectRatio * dpr;
-    canvas.getContext("2d").scale(dpr, dpr);
+    const size = canvas.parentNode.offsetWidth * 0.8;
+    canvas.style.width = size * dpr + "px";
+    canvas.style.height = size * dpr / aspectRatio + "px";
+    canvas.width = size;
+    canvas.height = size / aspectRatio;
     updatePlot();
 }
 

src/drawing/backend_impl/canvas.rs

@@ -73,12 +73,8 @@ impl DrawingBackend for CanvasBackend {
     type ErrorType = CanvasError;
 
     fn get_size(&self) -> (u32, u32) {
-        // Getting just canvas.width gives poor results on HighDPI screens.
         let window = window().unwrap();
-        let mut dpr = window.device_pixel_ratio();
-        dpr = if dpr == 0.0 { 1.0 } else { dpr };
-        ((self.canvas.width() as f64 / dpr) as u32,
-         (self.canvas.height() as f64 / dpr) as u32)
+        (self.canvas.width(), self.canvas.height())
     }
 
     fn ensure_prepared(&mut self) -> Result<(), DrawingErrorKind<CanvasError>> {